Electrical tone source for musical instruments



y 24, 1956 s. KRAUSS ET AL 2,756,339

ELECTRICAL TONE SOURCE FOR MUSICAL INSTRUMENTS Filed Oct. 7, 1950 l EN TORS.

ELECTRICAL TONE SOURCE FOR MUSICAL INSTRUMENTS Serge L. Krauss and Charles J. Tennes, Ellthart, Ind,

assignors to C. G. Conn Ltd., Elkhart, Ind, a corporation of Indiana Application October 7, 1950, Serial No. 188,990

9 Claims. (Cl. 250-36) This invention relates to electrical musical instruments and more particularly to tone generator circuits for electric organs.

it has been proposed in the patent to McKellip et al. 2,340,002 to derive tone frequency currents of two different characters from different parts of a single oscillator circuit. This circuit requires a tube having a screen grid and the screen grid is keyed to start and stop the oscillation. Tubes of this type are more expensive than triodes and add further complications to the circuit all of which increase its cost.

It is accordingly one of the objects of the present invention to provide a tone generator circuit for an electrical musical instrument which is relatively simple and inexpensive and which employs a triode tube to produce tone frequency currents of two different characters.

Another object is to provide a tone frequency generator circuit which is keyed in the anode and in which the attack and release characteristics can easily be controlled.

Still another object is to provide a tone frequency generator producing a pulse type wave in which the shape of the pulse can easily be adjusted. Preferably the pulse is a relatively sharp one and the adjustment changes the shape of its base line.

Another object is to provide a tone frequency gener ator in which desired amounts of the pulse frequency are added to the sine curve frequency.

A further object is to provide a tone frequency generator in which a tremolo voltage of adjustable amplitude is impressed on the generator. According to one feature the tremolo generator is constructed to produce a change in frequency in response to changes in amplitude.

The above and other objects and advantages will be more readily apparent from the following description when read in connection with the accompanying drawing, in which:

Figure l is a diagrammatic view of an electric organ embodying the invention;

Figure 2 is a circuit diagram of a single tone generating circuit;

Figure 3 is a diagram indicating the shape of the pulse wave; and

Figure 4 is a simplified circuit diagram of a portion of the circuit.

The instrument is of the type in which tone frequency currents of two different types are generated, mixed and amplified to produce tones of the type desired. As shown in Figure 1 pulse tones containing a large number of harmonies are generated by generators and flute tones consisting of substantially pure sine waves are generated by generators 11. It will be understood that a tone of each type is generated for each note on the instrument, there being 85 generators in a typical instrument.

The pulse generators are connected across a string control potentiometer 12 through which the amount of pulse tone desired can be selected and to a mixing resistor 13. The pulse generators are also connected through an isolating resistor 14 across a resonant reed atent f) ice control circuit shown as including a coil 15 and a variable condenser 16. A switch 17 may shunt the resonant circuit when no reed tone is desired. The resonant circuit modifies the form of the pulses to a shape similar to reed tone waves and supplies the modified pulses to a mixing resistor 18.

The mixing resistors 13 and 18 are both connected to the control grid of one section of a double triode mixing amplifier tube 19. The control grid of the other section is connected through a variable potentiometer 21 to the flute tone generators 11. The plates of the tube sections are connected through mixing resistors 22 and through a variable potentiometer 23 to the ground side of the circuit. An amplifier 24 is connected to the potentiometer 23 and drives a speaker 25 through which the tones are produced.

As shown the lower or bass tones are variably attenuated by a series condenser 26 shunted by a variable re sistor 27 in the mixer output circuit to control the relative volume of the bass tones. The treble tones are similarly controlled by a variable condenser 28 shunted across the potentiometer 23. These features are more particularly described and claimed in our copending ap plication Serial No. l92,094 filed October 25, 1950.

According to the present invention both the pulse current and the sine current for each note are generated by a single oscillator. As shown in Figure 2, each oscillator includes a triode tube having an anode 31, a cathode 32 and a control grid 33. The anode is connected through a condenser 34 to ground. The grid is connected through a condenser 35 to a tank circuit including a coil 36 and condenser 37 in parallel and to ground through a pair of series resistors 38 and 39. The cathode is connected by a wire 42 to a tap on the coil 36 and to ground through a portion of the coils and resistors 38 and 39. Thus, an energy transfer path is formed between the anode and cathode from which pulse currents can be derived. For this purpose a transformer 41 has its primary connected in shunt with the resistor 39 and the pulse voltage is developed across the secondary of the transformer.

The cathode 32 of the tube is also connected through a filter circuit including a resistor 43 and condenser 44 in series to ground. Sine Wave or flute current is derived from a section of the tank coil through this filter circuit by means of a connection 45 to a point between the resistor 43 and the condenser 44.

Bias is applied to the grid 33 through a grid resistor 46 which has a relatively high value, for example 1,000,- 080 ohms. The resistor 46 is connected to a wiper 47 movable over a resistor 48 which is connected in parallel with a condenser 49 in a bias network whose purpose will appear more fully hereinafter. As shown a positive bias is applied to the grid so that the tube will not cut off when the instantaneous value of the tremolo voltage is negative and for this purpose the upper end of resistor 48 is connected through a resistor 51 to a +B source indicated at 52. If a tremolo voltage is not to be used or if cut off is not objectionable the resistor 51 could be connected to ground or to a negative source.

To start the oscillator the plate 1-51 is connected through a plate resistor 53 and rceying switch 54 to the +B source 52. The resistor and condenser 34 control the rate of change of plate voltage and therefore provide a very simple leans to control the attack and release of the tone when the switch 54 is closed or opened.

A low frequency tremolo voltage may be impressed on the oscillator through the bias network when desired and for this purpose a low frequency tremolo generator is provided. As shown this generator includes a pair of triode tubes 55 having their plates connected to opposite ends of the primary winding of a transformer 56. The

grids of the tube are connected to ground through grid resistors 57 and 58 and are cross connected through condensers 59 to the primary of transformer 56. A condenser 61 is connected across the transformer primary as shown to form a resonant tank circuit therewith.

To vary the amplitude of the tremolo generator the cathodes of the tubes are connected to ground through fixed resistors 62 and 63 and shunt circuits around the resistor 63 may be closed by switches 65. Additional resistors 65 may be connected in parallel with resistor 63 upon closing of certain of the switches 64. Another advantage of this construction is that it produces an increase in frequency of oscillation as the amplitude is increased. This is a highly desirable feature since it is desirable to vary both the frequency and amplitude of the tremolo efiect together for substantially all types of musical renditions.

The tremolo voltage is impressed on the tone generator oscillator by connecting the secondary of transformer 56 across the resistor 48 as shown. By adjusting the wiper 47 any desired part of the generated tremolo voltage may be impressed on the grid 33 thereby enabling a full selection of tremulant amplitude from zero to the full amount being produced by the tremolo generator. At the same time adjustment of the wiper 47 produces a complementary adjustment of the grid bias to insure that the tube will not cut otf in response to an instantaneous negative value of the tremolo voltage.

With the oscillator as so far described the pulse voltage derived at the transformer 41 will have a form substantially as shown in full lines in Figure 3 with a flat base line. For different types of tones it is desirable to vary the base line of the pulse more or less toward the dotted line in Figure 3 to control the harmonic content of the tone and to vary its percussive attack characteristic. For this purpose a resistor 66 is connected between resistor 39 and transformer 41 and is adjustably engaged by a wiper 67 which is connected to the lower end of resistor 48.

The impedance of the bias network 8, 49 is small e. g. 2500 ohms) compared to the grid resistor 46 so that adjustment of the wiper 47 has a negligible effect on the base line shape and can be disregarded. With the wiper 67 at the left end of resistor 66 the A. C. current through resistor 39 and transformer 41 is the plate current pulse of the tube. When the tube is idle between pulses the grid condenser 35 Will discharge through resistor 46, resistor 48 and condenser 49 in parallel, to wiper 67, and through resistor 38 and the tank circuit 36, 37 to condenser 35. This flow of condenser discharge current through resistor 39 and transformer 41 is negligible and the flat pulse base line as shown in Figure 3 results.

With the wiper 67 at the right end of resistor 66, a part of the condenser discharge current will be impressed on the primary of transformer 41 when the tube is idle between pulses. This current flow is in phase opposition to the pulse current and will depress the pulse base line to the dotted line position. By connecting wiper 67 to resistor 39 instead of to resistor 66 the polarity of the potential impressed on the transformer 41 will be reversed and the base line of the pulse will curve upward instead of downward.

The resistor 38 is provided to add a small amount of pulse voltage to the sine wave voltage which is desirable,

by the resistor 30'. From this circuit it will be seen that the voltage between wire 42 and ground is equal to the voltage between the connection of wire 42 to the coil 36 and the bottom of the coil plus the voltage developed across resistor 38. The impedance of resistor 39 shunted by transformer 41 is negligible and that in coil 36 is relatively small so that the added pulse voltage is due primarily to resistor 38.

It will be seen that the present invention provides a relatively simple and inexpensive tone generator circuit having a high degree of flexibility and presenting a number of operating advantages. It is not, however, intended that the scope of the invention be limited to the exact form shown nor otherwise than by the limitations of the appended claims.

What is claimed is:

1. In an electrical musical instrument, a tone generator comprising an oscillator including an electron discharge tube, anenergy transfer path between the cathode and grid of the tube, a grid condenser connected in series in the path, an energy transfer path between the anode and cathode of the tube, an impedance in series in the last named path, a transformer connected across the impedance to derive tone frequency pulses from the path, a series resistance in the connection between one side of the transformer and one side of the impedance, a wiper adjustably engaging the resistance, and a connection from the wiper to the grid side of the grid condenser.

2. In an electrical musical instrument, a tone generator circuit comprising an electron discharge tube having a cathode, an anode, and a grid, a circuit connecting the anode and cathode, a resonant circuit connected to the grid of the tube including parallel inductance and capacitance elements a resistor in series with the resonant circuit and on the side thereof remote from the grid, means to derive tone frequency pulses from the first named circuit, means to derive sine wave tone frequency current from the resonant circuit, a connection from one side of the last named means to the side of the series resistor remote from the inductance and capacitance elements, and a tap on the inductance element connected to the other side of said last named means.

3. In an electrical musical instrument, a tone generator circuit comprising an electron discharge tube having a cathode, an anode, and a grid, a circuit connecting the anode and cathode, a resonant circuit connected to the grid of the tube including parallel inductance and capacitance elements a resistor in series with the resonant circuit and on the side thereof remote from the grid, means to derive tone frequency pulses from the first named circuit, a filter circuit connected to the resonant circuit across which sine Wave tone frequency currents are derived, and connections from the filter circuit to a tap on the inductance element and to the side of the series resistor remote from the inductance and capacitance elements.

4. In an electrical musical instrument, a tone signal generator circuit including in combination, an oscillator circuit including an electron discharge tube having a cathode, an anode and a control grid, a first energy transfer path between said anode and said cathode of the tube in which tone frequency signals are developed, output means including impedance means in said first energy transfer path for deriving tone frequency current therefrom, a second energy transfer path between said cathode and said grid of said tube, said second energy transfer path having therein an energy storing element to receive energy therefrom during flow of energy therethrough, and circuit means connecting said energy storing element to said output means for supplying energy to said output means when no energy is flowing through said first path, whereby the signal developed in said first path is combined with energy from said energy storing element to provide a modified signal at said output means.

5. In an electrical musical instrument, a tone signal generator circuit including in combination, an oscillator greases circuit including an electron discharge tube having a cath ode, an anode and a control grid, a resonant circuit connected to said cathode and said control grid, a first energy transfer path between said anode and said cathode and including at least a part of said resonant circuit in which tone frequency signals are developed, output means including impedance means in said first energy transfer path for deriving tone frequency current therefrom, a second energy transfer path between said cathode and said grid of said tube and including at least a part of said resonant circuit, said second energy transfer path having condenser means connected between said resonant circuit and said grid to receive energy from said second path during flow of energy therethrough, and circuit means connecting said condenser means to said output means for supplying energy from said condenser means to said output means, whereby the signal developed in said first path is combined with energy from said condenser means to provide a modified signal at said output means.

6. In an electrical musical instrument, a tone signal generator circuit including in combination, an oscillator circuit including an electron discharge tube having a cathode, an anode and a control grid, a resonant circuit connected to said cathode and said control grid, a first energy transfer path between said anode and said cathode and including at least a part or" said resonant circuit in which signals having pulse waveform are developed, output means including impedance means in said first energy transfer path for deriving tone currents of pulse waveform therefrom, a second energy transfer path between said cathode and said grid of said tube and including at least a part of said resonant circuit, said second energy transfer path having condenser means connected between said resonant circuit and said grid to receive energy from said second path during flow of energy therethrough, and circuit means connecting the grid side of said condenser means to said output means for supplying energy from said condenser means to said output means, whereby the signal developed in said first path is combined with energy from said condenser means to modify the waveform of the signal at said output means.

7. In an electrical musical instrument, a tone generator comprising an oscillator including an electron discharge tube having a cathode, a grid and an anode, an energizing circuit for said anode of said tube including a first impedance and a keying switch connected in series from a source of potential to said anode, an energy transfer path between said cathode and said grid of said tube with a grid condenser connected in series in said path, an energy transfer path between said anode and said cathode of said tube including a second condenser connected from said anode to a reference potential, a second impedance in series in said last named path, a transformer connected across said second impedance to derive tone frequency pulses therefrom, a series resistance in connection between one side of said transformer and one side of said impedance, a wiper adiustably engaging said resistance, and a connection from said wiper to the grid side of said grid condenser, the value of said first impedance being related to the value of said second condenser to provide desired attack and decay characteristics in response to operation of said keying switch.

8. in an electrical musical instrument, a tone generator comprising an oscillator including an electron discharge tube having a cathode, a grid and an anode, a source of positive potential, an energizing circuit for said anode of said tube including an impedance and a keying switch connected in series from said source of potential to said anode for selectively providing a positive potential thereon, a circuit connecting said anode and said cathode of said tube including a condenser connected from said anode to a reference potential, means for deriving tone frequency pulses from said iast named circuit, a resonant circuit connected to said grid of said tube including parallel inductance and capaci ce elements, a resistor in series with said resonant circuit and on the side thereof remote from said grid, at filter circuit conn' to said resonant circuit across which sine wave tone freuuency currents are derived, connections from said filter circuit to a tap on said inductance element and to the side of said series resistor remote from said inductance and capacitance elements, and bias circuit means connecting said source of potential to said grid of said tube to provide a positive bias on said grid prior to operation of said keying switch so that the oscillator responds rapidly upon operation of said keying switch, the value of said impedance being related to the value of said condenser to provide desired attack and decay characteristics in response to operation of said keying switch.

9. In an electrical musical instrument, a tone signal generator circuit including in combination, an oscillator circuit including an electron discharge tube having a cathode, an anode and a control grid, an energizing circuit for said anode of said tube including impedance means and a keying switch connected in series from a source of potential to said anode, a first energy transfer path between said anode and said cathode of said tube in which tone frequency signals are developed, output means including impedance means in said first energy transfer path for deriving tone frequency current therefrom, said first energy transfer path including condenser means connected from said anode to a reference potential, a second energy transfer path between said cathode and said grid of said tube, said second energy transfer path having therein an energy storing element to receive energy therefrom during fiow of energy therethrough, and circuit means connecting said energy storing element to said output means for supplying energy to said output means when no energy is flowing through said first path, whereby the signal developed in said first path is combined with energy from said energy storing element to provide a modified signal at said output means, the value of said impedance means being related to the value of said condenser means to provide desired attack and decay characteristics in response to operation of said keying switch.

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Radio Engineering, Terman, pp. 349-359, 1937. 

